3D printing of porous Si₂N₂O ceramics based on strengthened green bodies fabricated via strong colloidal gel

A convenient direct ink writing porous ceramic preparation strategy incorporating green body strengthening measure was provided. Different hydrogen bond interactions between particles in polar and nonpolar solvents have been successfully applied to regulate the rheological properties of 3D printing ink. Inks with different (NH₄)H₂PO₄ content were systematically optimized, which exhibited acceptable ambient stability and superior printing behavior. The phosphoric acid generated by decomposition of (NH₄)H₂PO₄ reacts with silica or oxide layer of silicon nitride to form Si–O–P binder by a pretreatment at low temperature to strengthen the green body. The compressive strength of green body fabricated by ink with 0.2 g/mL (NH₄)H₂PO₄ was increased by 415%. The Si₂N₂O single wall frame structure parts with a compressive strength of 3.33 ± 0.14 MPa under a frame density of 1.14 ± 0.05 g/cm³ were fabricated. The dielectric constants of the developed ceramic parts range from 3.57 to 4.21. A systematic study of design and preparation of ink and quantization of molding parameters provide a reference for in-situ reinforced the ceramic green body of silica, silicon nitride and their composites, as well as fabrication of their corresponding highly porous ceramic components based on the direct ink writing.